Laser neutron production depends on the use of intense, short pulse width laser radiation to produce thermonuclear reaction or "burn" in an appropriate fuel. The laser radiation causes the fuel to literally implode upon itself, thereby producing a density in temperature at which the burn can effectively occur. Ideally, the most efficient burn should be created by a perfectly spherical symmetric implosion of the fuel. This requires the fuel to be present in a spherical form and to be irradiated simultaneously and uniformly about its entire outer periphery or the outer periphery of its spherical container.
One type of target structure and method of its preparation is taught in U.S. Pat. No. 4,038,125 to Fries et al. The Fries et al. patent teaches a laser target constructed on a thin plastic film on the order of 500 .ANG. in width. Although this type of target structure is highly suitable for use, there are times when plastic is not desirable inside the shell. Furthermore, such a target is not glued together but is fabricated utilizing a thermosetting plastic.
The most common type of laser target structure at present comprises a microballoon and at least one surrounding shell affixed to a single stalk. This structure requires micromanipulation within three dimensions to position and hold the shells while the glue sets. Fabrication of a single target is difficult and time consuming requiring two microscopes for assembly. The diameter of the stalk is on the order of 5 to 10.mu..
In fabricating a target on a stalk, a first plastic spherical shell is cut into hemispheres and a 10 .mu.m hole is drilled near the pole of one of the hemispheres. A stalk is selected and its 5 .mu.m tip is ground flat perpendicular to its longitudinal axis. The 5 .mu.m flat tip of the stalk is inserted through the 10 .mu.m hole in the drilled hemisphere and is positioned 50 .mu.m away from and pointed at the center point of the hemisphere. The drilled hemisphere is then glued to the stalk and a microballoon is glued to the tip of the stalk so that it is positioned at what will be the center of the sphere formed when the undrilled hemisphere is glued to the drilled hemisphere to form a sphere about the microballoon. The edges of the undrilled hemisphere are then aligned with the edges of the drilled hemisphere and glued thereto.
The target structure which is the subject of the instant invention is useful in producing neutrons. Several references which illustrate the use of and describe such targets are "More Evidence That Fusion Works" by Harlow G. Ahlstrom and John F. Holzrichter, Laser Focus, Sept. 1975, Vol. 11, No. 9, page 39 et seq., "Laser-Driven Compression of Glass Microspheres," P. M. Campbell et al., Physical Review Letters, Vol. 34, No. 2, Jan. 13, 1975, pages 74-77, "Double-Shell Target Designs for the Los Alamos Scientific Laboratory Eight-Beam Laser System," Joseph M. Kindel and Michael A. Stroscio, LA-7167-MS, March 1978, "Spatially Resolved .alpha. Emission from Laser Fusion Targets," N. M. Ceglio and L. W. Coleman, Physical Review Letters, Vol. 39, No. 1, July 4, 1977, "Implosion Experiments With D.sub.2, .sup.3 He Filled Microspheres," V. W. Slivinsky et al., Preprint UCRL-78450 Rev. 1, Mar. 11, 1977, and "Laser-Fusion Ion Temperatures Determined by Neutron Time-Of-Flight Techniques," R. A. Lerche et al., Preprint UCRL-79375, April 1977.
One object of the present invention is to simplify the assembly of laser target structures.
Another object of the present invention is to provide for relatively easy accurate assembly of multi-shell targets.
One advantage of the present invention is that the shells surrounding the microsphere need only be manipulated in two dimensions in order to center the microsphere within the shell during target fabrication.
Another advantage of the instant invention is that the target constructed in accordance therewith is relatively free of undesirable constituents within the shell assembly.